But those on the Multnomah County side of the line never got the call.

"We can only verify that the reverse call went out to those in Clackamas," said Steve McAdoo, spokesman for Clackamas Fire District. "I'm not sure a call went to Portland."

It didn't and as of Thursday, Portland Emergency Management had little explanation.

"We have a community notification system in place called First Call that reaches landlines," said Dan Douthit, interim spokesman. "Unfortunately, yesterday the message did not go out but it is something being looked into right now."

Joe Campbell, treasurer of the Ardenwald Johnson Creek neighborhood association, said knew something was wrong when helicopters began flying over the area. "We weren't ever notified and didn't know for sure until we turned on the television," Campbell said.

The incident started Wednesday with a power outage at Precision Castparts, located where boundaries for Milwaukie, Portland and unincorporated Clackamas County converge on Southeast Johnson Road.

The plant, which makes aircraft parts, washes titanium in a bath of water, nitric acid and hydrofluoric acid, Department of Environmental Quality officials said. Normally, fumes would be drawn through an exhaust fan and into a wet scrubber that removes 98 percent or more of the pollutants before being released.

On Wednesday night, after the electricity went out, the company switched to a backup generator but was unable to power up the pollution control equipment, resulting in release of a cloud that consisted of hydrofluoric acid, nitric acid fumes and nitrogen dioxide, according to incident reports and DEQ officials.

Precision Castparts has a permit to release air pollutants below levels established in the Clean Air Act. In 2010, it reported releases of 126 tons of pollutants, including 53 tons of volatile organic compounds and 24 tons of nitrogen dioxide. The incident Wednesday is considered an "excess" release said Greg Grunow, a DEQ air quality inspector.

If a the DEQ determines the release was avoidable, the company could be fined.

Precision Castparts spokesman Dwight Weber says the company has a "very good safety program and good safety record." However, Melanie Mesaros , spokeswoman for Oregon OSHA said her organization has cited and fined Precision four times since 2006, mostly for electrical issues. A new investigation was launched Thursday.